/*
 * Safe-threaded singleton
 *
 * Copyright (c) 2008, Radist <radist.nt@gmail.com>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *     * Redistributions of source code must retain the above copyright
 *       notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above copyright
 *       notice, this list of conditions and the following disclaimer in the
 *       documentation and/or other materials provided with the distribution.
 *     * Name(s) of contributor(s) may not be used to endorse or promote products
 *       derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY Radist ''AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL Radist BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#ifndef __SINGLETON_TEMPLATE__H__R___
#define __SINGLETON_TEMPLATE__H__R___

#include "threads.h"
#include <memory>

template<class _Sy>
class SingletonThr
{
	static std::auto_ptr<volatile _Sy> instance;
	static CriticalSection cs;
	SingletonThr(SingletonThr&) {}
protected:
	SingletonThr() {}
	~SingletonThr() {}
public:
	static _Sy &GetInstance(void);
};

template<typename _Sy> std::auto_ptr<volatile _Sy> SingletonThr<_Sy>::instance;
template<typename _Sy> CriticalSection SingletonThr<_Sy>::cs;

template<class _Sy>
_Sy &SingletonThr<_Sy>::GetInstance(void)
{
	//Visual Studio inserts memory barriers before reading and after writing volatile variables.
	//Probably, this source will not work for old VS versions, other compilers/platforms.
	if (instance.get())
	{
		return (_Sy&)*instance;
	}
	Locker lock(cs);
	if (!instance.get())
	{
		instance.reset(new _Sy());
	}
	return (_Sy&)*instance;
}

#endif//__SINGLETON_TEMPLATE__H__R___
